What Is Continuous Glucose Monitoring CGM? | Basics & Models

What is continuous glucose monitoring (CGM)? It is a wearable system that reads your glucose automatically every few minutes through a tiny sensor just under the skin, sending real-time data to your smartphone. This replaces the old approach of pricking a finger at random moments and hoping the number still matters twenty minutes later. For anyone managing diabetes—or simply curious about how diet and activity affect their metabolism—a CGM provides feedback a fingerstick alone cannot match.

How Does a CGM Work?

A CGM has three parts: a disposable sensor, a transmitter, and a display (usually a smartphone app). The sensor is a thin filament inserted just beneath the skin that reads glucose in the interstitial fluid. The transmitter sends that reading wirelessly to the app, which shows your current number, a trend arrow, and a history graph covering the past 24 hours.

Sensors last 10 to 15 days depending on the brand, then need replacement. Applying a new one takes about a minute using a spring-loaded applicator—most users describe the insertion as quick and nearly painless. Once active, readings arrive every 1 to 5 minutes, giving you a near-continuous picture of where your glucose is and where it is heading.

How Is a CGM Different From a Fingerstick?

A fingerstick measures blood directly from a capillary puncture. A CGM reads from the interstitial fluid, which lags behind blood glucose by 5 to 15 minutes. That lag is most noticeable when glucose is rising or falling rapidly—after a carb-heavy meal or during intense exercise. Per Cleveland Clinic’s guide on CGM, this lag means you still need a fingerstick to confirm any reading that appears low, but the CGM provides patterns and trends a single blood test cannot reveal.

The Four CGM Models Available in 2026

Four FDA-cleared CGM systems are available in the US as of 2026. Two require a prescription (Dexcom G7 and FreeStyle Libre 3+), and two are sold over the counter (Dexcom Stelo and Abbott Lingo). Previous-generation models such as the FreeStyle Libre 2 and Dexcom G6 are still used by some patients.

The critical difference between prescription and OTC models: only prescription CGMs include alarms for high and low glucose levels. If you need those alerts for safety—especially overnight—choose a prescription model.

Prescription vs. Over-the-Counter: Key Differences

The choice between a prescription CGM and an OTC model goes beyond whether you need a doctor’s order. The table below breaks down the practical differences.

Dexcom Stelo is the only OTC model that lets you share data directly with your healthcare provider. Abbott Lingo makes sharing more difficult, so if your doctor wants to see your trends, Stelo is the better OTC pick.

If you have diabetes and rely on low-glucose alerts to prevent dangerous episodes, stick with a prescription CGM. If you simply want to track your glucose for general health, metabolic insights, or fitness optimization, an OTC model works—and for those without diabetes, our guide to CGMs for non-diabetic users covers the best options by price and feature set.

How to Use a CGM Correctly

Applying a CGM takes about two minutes after you have done it a few times. The steps are similar across all four models:

1. Wash the application site with soap and water. Use the back of the upper arm (Libre systems) or the abdomen (Dexcom systems). Avoid areas with lotion, scars, tattoos, or stretch marks.
2. Press the applicator firmly against the skin and release the button. The filament inserts automatically with a spring-loaded mechanism.
3. If the model uses a separate transmitter, snap it into the sensor housing. Some models are all-in-one with no separate transmitter.
4. Open the smartphone app and follow the on-screen pairing prompts. The sensor begins reading after a 30- to 60-minute warm-up period.
5. Set your target glucose range and customize alarm thresholds in the app (prescription models only).
6. Replace the sensor when the app indicates it has expired. Rotate the application site each time to reduce skin irritation.

After the warm-up, your app displays a current glucose number, a trend arrow showing direction and speed of change, and a graph covering the past 24 hours. Readings update every 1 to 5 minutes depending on the model.

Common Mistakes and Safety Caveats

The most frequent mistake new CGM users make is trusting a low reading without checking it against a fingerstick. Because CGMs measure interstitial fluid rather than blood, they can read up to 15 minutes behind, and accuracy drops at the low end. Treating a false low can lead to overtreating and a subsequent high.

False alarms are another common frustration. Sensors can give erratic readings if the adhesive is not fully seated, if the sensor is compressed during sleep, or if the device simply fails. Replace any sensor that consistently reports numbers that contradict how you feel.

OTC models lack alarms entirely. If you choose Dexcom Stelo or Abbott Lingo, you will not receive a notification when your glucose goes too high or too low. For anyone at risk of hypoglycemia, an OTC CGM without alarms is not a safe choice unless you check the app regularly throughout the day and night.

Who Benefits From Continuous Glucose Monitoring

Prescription CGMs with alarms are the standard of care for anyone with Type 1 diabetes and are increasingly recommended for Type 2 patients, particularly those using insulin. For people with prediabetes or metabolic syndrome, an OTC CGM can reveal how different foods, sleep patterns, and exercise routines affect glucose levels through the course of a day.

Athletes and fitness enthusiasts also use CGMs to test nutritional strategies and optimize performance, though the evidence for specific athletic protocols is still emerging. Non-diabetics interested in metabolic tracking typically choose between Stelo and Lingo. The decision comes down to whether sharing data with a provider matters—if it does, Stelo wins.